1. Field of the Invention
Embodiments of the invention generally relate to electrochemical cells and more particular to flow battery cells and systems.
2. Description of the Related Art
Flow batteries containing electrochemical cells have been around for several decades and are used to store electrical energy. Although a variety of flow batteries exist in the art, a couple of known types of flow batteries include the zinc-ferrocyanide battery and the zinc-bromide battery. When these types of battery cells are charged, a metal (e.g., zinc) is plated onto a planar electrode within the battery cell. For an efficient battery cell, the metal should be plated at an acceptable rate, uniformity, volume, and morphology. An important aspect with flow batteries is that all or substantially all of the metal plated onto the planar electrode is available for deplating during the discharge of the battery cell. For example, metal plated with a morphology that has poor adhesion may fall off the planar electrode before the electrical discharge and the energy stored while plating this metal would be lost.
Furthermore, a current density distribution created during plating (e.g., metal thickness uniformity) that is different than the current density obtained during the discharge leads to non-uniform metal build-up over many charge/discharge cycles. As a result, the metal will be depleted down to the electrode in some regions and not in others, possibly leading to gas evolution, higher cell potentials, and/or reduced battery efficiency. Flaked or deplated metal particles which accumulate in the battery cell may block the electrolyte flow paths or channels, enter and contaminate the electrolyte membrane, or cause other problematic issues—if left without intervention (e.g., removal of the flaked metal). Similarly, metal plated onto certain portions of the electrode and not subsequently deplated may build up over many charge cycles of the battery causing issues such as flow blockage, shorting, or membrane damage.
Additionally, the compact nature of a typical flow battery cell generally creates challenges to obtaining optimal plating performance. The typical flow battery cell often has electrodes with a large surface area separated by small gaps to minimize cell ohmic resistance (for higher battery efficiency) and to keep a plurality of flow battery cells packed within a dense array. As a result, the flow path for the electrolyte is restricted to a narrow channel which makes it difficult to provide a uniform, high rate of ion replenishment across a large surface area electrode. Also, ion replenishment can be increased with higher electrolyte flow rates, but it is desirable to keep pumping flow rates and pressure losses (pump energy requirements) as small as possible to keep the battery efficiency.
Therefore, there is a need for a flow battery cell having an improved ion replenishment (e.g., mass transfer) to the electrode surface to provide metal plating at increased rates, volumes, uniformity, and morphology over a traditional flow battery having a planar electrode.